In recent years, a P2P (Peer to Peer) system has been generally known, in which a plurality of unspecified computers are connected to each other through a network and directly transmit and receive contents.
In this system, a time that is expended to download the contents means a waiting time for a user. In particular, file sizes of the contents, such as moving pictures, are generally large. A time that is expended for the user to view the contents significantly decreases the user's convenience.
As a method of increasing a user's convenience, there is a method in which contents are downloaded in advance (before the user views the contents). For example, according to a method discussed in Japanese Unexamined Patent Application No. 2007-104656, an HTTP (HyperText Transfer Protocol) proxy server exchanges a function of intermediating download requests from a plurality of users, caches the contents that are already downloaded and exchanged to another user, and exchanges the caches according to the download requests from the users, thereby shortening a download time.
According to Japanese Unexamined Patent Application No. 2006-325011, a technology is discussed for downloading contents of a Web site of a cyclic object registered in advance by a user in an available time and using the downloaded contents when the contents are actually used.
Further, the following method has been known. In a P2P network, among a plurality of existing nodes of download destinations, a node where contents can be downloaded in a short time is selected on the basis of path and band information of the network or a load situation of the node, and the contents are downloaded from the selected node.
However, since there is a limitation in a capacity of a storage area where contents are accumulated or a network band occupied to download the contents in advance, the storage capacity or the network band may be wasted if unnecessary contents are also downloaded in advance. As a result, efficiencies of the storage capacity and the network band are deteriorated.
Further, when the node of the download destination in the P2P network is selected, an effect of shortening a download time for an individual content is obtained. However, since it is not determined whether the individual contents are necessary or unnecessary, the unnecessary contents may be downloaded.